Multiple spindle bar or chucking machines have long been known in the art. Representative designs of multiple spindle machines are found in U.S. Pat. Nos. 1,664,742 to Doan, 4,048,082 to Link, and 3,735,460 to Crachy et al.
As disclosed in the Doan patent, multiple spindle machines typically include a rotatable turret that carries a plurality of spindles for holding workpieces. Each spindle includes a chuck operated by compressed air that may be actuated to securely engage a workpiece and hold it in position for machining. The rotatable indexing turret is locked in position by means of a locking bolt or pin that is biased by a spring so as to engage a notch in the turret. The individual spindles may also be prevented from rotating by engagement of projections or pins in cooperating notches of a plate keyed to the spindle.
Despite the existence of a large number of multiple spindle machine designs in the art, further improvements in construction and many operating characteristics are still desired.